The plant enzyme that helps make broccoli so good for you survives the acid in your stomach

Posted July 6, 2019byTeresa Johnson

A team of scientists led by Dr. Jed Fahey of the Cullman Chemoprotection Center investigated whether stomach acidity influences the activity of myrosinase, a type of enzyme. Myrosinase plays a role in the production of sulforaphane, a beneficial plant compound derived from broccoli and broccoli sprouts. The findings were posted online June 29, in the journal Nutrients, and will appear later this year in their special issue, “Plant Food, Nutrition, and Human Health.”

Myrosinase is found in the leaves and stems of broccoli and broccoli sprouts. Chopping, chewing, or otherwise damaging the plants causes a reaction between myrosinase and another broccoli-plant chemical called glucoraphanin, a powerful indirect and long-lasting antioxidant. The end product of the reaction is sulforaphane, which switches on a vast array of protective responses in the human body that reduce the risk of developing many chronic diseases. Sulforaphane is what gives broccoli its slightly pungent flavor.

Glucoraphanin and myrosinase derived from broccoli sprout extracts are widely available in dietary supplements in the form of capsules or tablets. These preparations are used in the research setting and are also sold commercially. Although glucoraphanin is fairly stable in the human gut, myrosinase is vulnerable to breakdown by the acid in the stomach, limiting its ability to convert glucoraphanin to sulforaphane.

Myrosinase is also found in the human gut, however. It is produced by the commensal, or “friendly,” microbes that reside there. Myrosinase in the gut can convert ingested glucoraphanin to sulforaphane, albeit to varying degrees, due to variations in the gut microbial make-up among different individuals. “Gut conversion of glucoraphanin to sulforaphane ranges from about 1 to 40 percent,” said Dr. Fahey.

Many people take proton pump inhibitors, a class of drugs that reduce the amount of acid produced in the stomach. Proton pump inhibitors are used to treat gastroesophageal reflux disease (commonly known as GERD), as well as peptic ulcers and other digestive disorders. They are available by prescription or over-the-counter.

The team of researchers conducted a study to determine whether stomach acidity would affect the activity of myrosinase that was co-delivered in a dietary supplement containing glucoraphanin. The study involved 16 healthy adults of varied ages, races, and other demographics. Each participant took the dietary supplement either with or without a proton pump inhibitor. Afterward, the researchers collected urine samples from the participants to determine how much sulforaphane they excreted – an indicator of how active the myrosinase was.

They found that delivering myrosinase and glucoraphanin together in the form of the commercially available supplement Avmacol® markedly increased sulforaphane production among the participants, with approximately 32 percent of the glucoraphanin being converted to sulforaphane metabolites, regardless of the participants’ ethnicity, sex, body fat, vegetable consumption, or bowel movement frequency. Taking a proton pump inhibitor had a relatively minor effect on sulforaphane production. The researchers also noted that blood-markers of cellular protective responses were slightly elevated even after a single dose of the supplement.

“This is the first time that anyone has investigated whether people who take proton pump inhibitors for GERD – a sizable portion of the population – will get any benefit from these supplements,” said Dr. Fahey. “Taken together, these findings showed that providing active myrosinase and glucoraphanin together in a high-quality dietary supplement gave similar results to our previous clinical findings with material produced here at the Cullman Chemoprotection Center.”

Teresa L. Johnson, MSPH, RD, is a freelance science writer and health communications consultant with a long-time interest in the role of plant-based diets and cancer prevention. Her work draws on elements of nutritional biochemistry, phytochemistry, and epidemiology.